From PerlNet

Under Win32 systems, the chain of calls for a system() command is as follows:

• pp_sys.c : pp_system invoked
• win32/win32.c : do_aspawn() invoked
  • do_aspawn appears to always want to use the shell.
• win32/win32_spawnvp does the hard work
• CreateProcess ultimately brings the process to life.

Alternatively, pp_sys.c may invoke do_spawn() from win32.c, under conditions I'm yet to interpret.

• do_spawn invokes do_spawn2 in win32.c
• do_spawn2 checks for shell metachars
• If no metachars present, tries to execute the command directly.
• If the command fails, or metachars present, tries to execute the shell with the given command.
  • This may be a bug, resulting in multi-arg system() invoking the shell.
• win32_spawnvp still ultimately does the work